1. Field of the Invention
The present invention relates to a contact fixing device used primarily in electrophotographic copiers for fixing a toner image on a sheet material.
2. Description of the Prior Art
European Patent Application No. 0149860 which corresponds to U.S. Pat. No. 4,706,947 describes a contact fixing device for fixing a toner image on a sheet material. In this device, toner and other material which adheres to the fixing surface is taken up by the cleaning roller. Thus, a toner layer gradually forms on the surface of the cleaning roller and is subject to pressure as it passes through the nip between the cleaning roller and the fixing surface. As a result of the pressure in the nip, toner is forced through the perforations and into the interior of the cleaning roller.
The toner taken up by the cleaning roller is distributed uniformly over the roller surface by the pressure in the nip. The pressure distributes the toner material in all directions on the cleaning roller. Toner situated on the roller near its ends will move laterally over the roller surface under this pressure and will flow over those ends and contaminate the device as it becomes detached from the roller. It would be desirable to have a device which obviates this contamination.
U.S. Pat. No. 4,411,042 describes a toner cleaning apparatus used in a contact fixing device which could have the shape of a perforated roller. Residual toner particles on the fixing surface are scraped off by the edge portions of the perforations and fall into a receptacle in the interior of the cleaning apparatus. With this cleaning apparatus, there is nothing to prevent the toner material from moving laterally over the cleaning surface and eventually flowing over the ends of the cleaning device causing contamination as described above.
U.S. Pat. No. 3,649,992 discloses another cleaning apparatus used in a contact fixing device which does not employ a perforated cleaning roller. Instead, it uses a plurality of washer-shaped rollers upon which the toner particles cool and solidify forming a layer. When the layer of toner particles builds up on the rollers, the rollers are replaced. The end caps only hold the washershaped rollers in place and do not press against the fixing surface. If toner builds up quickly in this device, the rollers will need to be replaced very often causing inefficiency.
A still different cleaning system used in a contact fixing device is described in U.S. Pat. No. 4,165,173 which is equivalent to German Patent Application No. 2,744,555. This system utilizes a first scraper blade for removing residual toner particles from the surface of a photosensitive drum, a resilient unperforated transfer roller which picks up the removed toner particles but does not press against the photosensitive drum and a second scraper blade which removes toner particles from the transfer roller surface. One disadvantage with this system is that the scraper blades can damage the transfer roller. Additionally, not all of the residual toner is removed because the transfer roller does not press against the photosensitive drum.